The present invention relates to a process for preparation of aluminoxane, and more particularly to a process for preparing in a simplified manner high purity and high active aluminoxane which is suitable as a catalyst component for production of olefin polymers, styrene-based polymers and so on.
A process for production of olefin polymers or styrene-based polymers by polymerization of olefins or styrene in the presence of a catalyst comprising (A) a transition metal compound and (B) aluminoxane has heretofore been known (Japanese Patent Application Laid-Open Nos. 36390/1987, 95292/1984, etc.).
In accordance with the process disclosed in Japanese Patent Application Laid-Open No. 36390/1987, in preparation of the above aluminoxane, a filtrate obtained by filtering off a solid material from a condensation reaction mixture of an organoaluminum compound and water is allowed to stand, and in the process disclosed in Japanese Patent Application Laid-Open No. 95292/1984, a solvent having a lower boiling point than the starting material of organoaluminum compound, such as toluene or heptane is merely distilled away at room temperature.
The reaction mixture contains an unreacted organoaluminum compound ineffective as a catalyst component along with chain or cyclic aluminoxane. If aluminoxane is prepared in a low boiling point solvent as described above, even after separation of the solvent, the unreacted organoaluminum compound remains undistilled away and pure aluminoxane cannot be obtained.
The present inventors have already proposed a process for obtaining pure aluminoxane in which the unreacted organoaluminum compound is removed by condensing a filtrate after reaction of the organoaluminum compound and water and, thereafter, heat treatment is applied under atmospheric pressure or reduced pressure (Japanese Patent Application No. 66910/1988).
In this process, however, since aluminoxane is obtained as a viscous liquid or a glassy uneven solid at an intermediate stage of heat treatment under reduced pressure, it is difficult to apply uniform heat treatment on an industrial scale and, therefore, an unreacted organoaluminum compound cannot be completely removed.
In utilization as a catalyst of the aluminoxane obtained by the above process, a step to dissolve the aluminoxane in a suitable hydrocarbon solvent or to prepare a slurry containing the aluminoxane is needed, which is undesirable for its commercial practice.
Although aluminoxane is expensive as a catalyst component, high purity aluminoxane has not been obtained as described above. Low purity aluminoxane has a disadvantage of being poor in catalytic activity when used as a catalyst component in production of olefin polymers or styrene-based polymers.